System and method for making polyethylene terephthalate sheets and objects

ABSTRACT

A sytem for making PET objects including a means for reacting a first PET precursor and a second PET precursor to produce a PET melt; a means for flowing the PET melt to a valve having at least two outlets; a means for flowing the PET melt from at least one of the at least two outlets to at least one distribution manifold, each of the at least one distribution manifold having at least two distribution lines; a means for controlling individually the mass flow of the PET melt in each of the at least two distribution lines independently of the other of the at least two distribution lines; and a means for forming the PET objects from the PET melt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of prior U.S. patent application Ser.No. 11/270,314, filed 8 Nov. 2005, which claims the benefit of U.S.Provisional Application No. 60/626,142, filed 8 Nov. 2004. Theentireties of these aforementioned applications are incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to a system and method for makingpolyethylene terephthalate sheets and objects.

Problem

As outlined in U.S. Pat. No. 5,756,032, polyesters such as polyethyleneterephthalate (“PET”) are known to possess good chemical stability,physical and mechanical strength, durability, and heat resistance.Therefore, polyester has been widely used in manufacturing variousarticles including packaging and labeling devises. The performanceappeal of polyester is very important and the ability to reduce the costof materials using this polymer will greatly expand its use. Polyesteris ranked between general purpose and engineering plastics and has beenproven to be used for many applications. Polyester packaging materialsin sheets is increasingly expanding and has a tendency to penetrateapplications it had not been identified with. Consequently, thebreakthrough to reduce its manufacturing cost for PET sheet applicationsand increase its mechanical and optical performance attributes for agreat array of applications is an important step in meeting the cost andperformance hurdles against competitive polymers and thereby expandingits attractiveness for new applications. Particularly, stiffness andimpact performance of the PET sheet is an important functional attributeas it allows for the PET sheet caliper to be reduced. These sheets canbe converted into rolls of different diameters or directly slit intosheets. PET and amorphous polyethylene terephthalate (“APET”) resin areused interchangeably as the resin used to manufacture the APET rigidfilm.

Under the traditional manufacturing process, a multi-stage process isused to produce the final PET or APET product. Initially, a relativelylow molecular weight precursor polymer is prepared by melt-phasepolymerization techniques commonly known in the art. As explained inU.S. Pat. No. 5,736,621, the customary route for the manufacture ofpolyester resin comprises polycondensation, the first step being carriedout up to a moderate molecular weight corresponding to an averageintrinsic or inherent viscosity (“I.V.”) of about 0.5-0.7deciliters/gram (“dl/gm”) in the melt and further condensation beingcarried in the solid phase. For condensation in the solid stage, thepolyester chips are heated under reduced temperature until the desiredmolecular weight is reached.

The precursor is then cooled and shaped into pellets, and then possiblycrystallized, and subjected to further solid-state polymerization at alower temperature. Gases may be used to strip the glycols, aldehydes,and other reaction byproducts from the PET pellets, which alsocontributes to increasing the I.V. value. This is followed by the PETpellets being commonly stored in ambient air where the hygroscopicpellets pick up moisture from the air, thus requiring the pellets to bedried before they are reheated and melted in an extruder incommunication with a die. Typically, the PET pellets are dried to lessthan 0.025% moisture content. If resin is dried prior to delivery to thesheet plant, the material will have to be stored under dry nitrogen.

The means for preparing the PET sheets from various forms andviscosities of PET has been known to require the use of PET pellets.Each quality of PET resins have problems of their own as a result of thePET material's hydroscopicity and its deterioration during the extrusionprocess. Such technique; however, requires the use of intermediatemanufacturing processes and transportation. Items produced using theextrusion system or rotary die method produce parts of varied calipers.

The resin is extruded through an extruder, and the barrel of theextruder may have vacuum venting in order to remove the humidity createdduring the extrusion process. A melt pump is used in order to produce aneven melt throughput as it is pushed towards the extrusion die. Next,the molten resin is formed into a sheet by passing through an extrusiondie. In the case of the rotary die, the objects are manufactureddirectly onto the rotary die and do not pass through the sheet phase.The sheet is then polished in a roll stack or passed through a calendarstack where the sheet is sized to the appropriate thickness. The sheetcan then be surface treated with silicone on one or both sides. In thecase of strapping material, the sheet is typically slit into strappingmaterial. Finally, the sheet is then wound into a roll or slit and cutinto finished sheets. In the case of the thick sheets, the sheets aretypically not rolled.

These various processes affect the PET pellets performance when they areconverted into a sheet form or injected onto a rotary die. In generalthe physical properties of PET, such as its hygroscopicity in pelletform, negatively impact the polyester optical properties of the finishedproduct if not adequately conditioned. When extruded, side reactionslead to the degradation of the polyester chain negatively impacting theproperties. Furthermore, it has been a common practice to compensate forsome of PET pellets negative performances as pertaining to thehydroscopicity and degradation the I.V. levels during the extrusionprocess.

In addition, during the processing of polyesters in the melt phase,certain undesirable by-products are formed. One such by-product isacetaldehyde, which is continually formed as a by-product during thepolymerization and subsequent melt processing of polyesters.Acetaldehyde is known to contaminate food or beverage products when itis present in a food or beverage container. Therefore, it is desirableto produce molded polyester containers having an acetaldehyde content ata low or zero level.

Additionally, there are methods decribing tying a reactor to a ramsystem to inject polymer into a mold. Other patents allude to acontinuous system but do not allow for uniform part production inmultiple streams.

Information relevant to attempts to address these problems can be foundin the U.S. Pat. No. 5,656,719 issued 12 Aug. 1997 to Stibal et al.;U.S. Pat. No. 5,980,797 issued 9 Nov. 1999 to Shelby et al.; U.S. Pat.No. 5,968,429 issued 19 Oct. 1999 to Treec et al.; U.S. Pat. No.5,756,032 issued 26 May 1998 to Stibal et al.; U.S. Pat. No. 6,099,778issued 8 Aug. 2000 to Nelson et al; and published U.S. patentapplication Ser. No. 10/996,352 filed 14 Oct. 2004 by Otto et al.

Solution

The above-described problems are solved and a technical advance achievedby the present system and method for making a mono or multilayerpolyethylene terephthalate (“PET”) sheets (“system for making PETsheets”) at a lower cost and which display excellent mechanical andoptical properties by way of eliminating certain manufacturing processsteps and directly passing the PET melt from the reactor through a dieand onto a surface instead of melting PET resin in pellets through anextruder and then onto a surface. By avoiding a series of manufacturingsteps whereby the PET melt is conditioned and altered during thepreparation and extrusion process the optical and mechanical propertiesof the original PET melt coming out of the reactor does not deteriorateor capture humidity. These are very important steps as theseintermediary steps above are eliminated as the PET resin is already in amelt phase and therefore does not have to be melted down through anextruder and also because no transportation was required which becauseof the hygroscopic nature of the pellet required a treatment ofnitrogen. In addition, the multiplayer PET may be manufactured usingother substrates in one or more of the layers. The present system formaking PET sheets allows for the preparation of particularly highquality PET sheets under mild reaction conditions since the PET is neverconverted into pellets and re-melted through an extruder.

The present system for making PET sheets which can be effectivelythermoformed into containers as well as slit into strapping material andwhen prepared into thick sheets can be used for display material forinside and outdoor signage. As the present system for making PET sheetspertains to the manufacture of items directly from the extruder die ontoa sheet forming system or a rotary die, the results are the same, asuperior product at a lower caliper without passing through the pelletstage, thus maintaining its I.V. level and inherent stiffness thattranslates into a higher mechanical performance. The present system formaking PET sheets is a process by which a continuous PET reactor systemis coupled to a series of forming subsystems while maintaining constantpressure in each subsystem independent of the operating conditions ofthe other subsystems. Thus speed changes, start-ups, shut-downs, andbreak downs are all overcome by the present system for making PETsheets.

In one aspect, the present system for making PET sheets extrudesproducts such as sheets or objects with a rotary die directly from PETmelt prepared from the polymerization reactor. The uniqueness of thispresent system for making PET sheets is in the handling of the meltstream from the reactor to the die. In order to extrude the melt througha die and maintain part thickness control, rigid control of the pressureentering each die needs to be maintained at a uniform set pressure andwithin tight tolerance. The present system for making PET sheets appliesto controlling pressure into the die(s) feeding the forming device(s). Aside chip stream is added to the multiple forming lines as well as aplurality of pumps prior to the die(s). These novel additions allow foruniform part formation.

The present system for making PET sheets produces high quality PETsheets in continuous and discontinuous forms wherein the PET melt isobtained directly from the esterification and after the polymerizationstage in the PET reactor using Pure Terephthalate Acid (PTA) or DimethylTerephthalate (DMT) and Mono Ethylene Glycol (MEG) and passed throughthe die directly onto a receiving surface without being converted intopellets. In another aspect, other types of glycols may be used, such asdiethylene glycol and the like. PET sheets produced by the above methodsare manufactured at a lower cost, have a high structural homogeneity,enhanced optical properties and excellent mechanical strength. In thecase of the manufacture of items directly from the reactor onto a rotarydie, the results are the same, except the products manufactured are notpreviously converted into sheets, but formed into their finalconfiguration.

In addition, the extruder, when coupled to a melt reactor andappropriately controlled, provides a material requiring nopreconditioning and whose thermal history is minimized. This couplingsimplifies the process and leads to a better finished product. Thenegation of intermediate process steps, such as pelletizing and drying,reduce the overall manufacturing cost. Furthermore, the present systemfor making PET sheets simplifies the manufacturing process tomanufacture PET sheets and items on a rotary die where the polymer doesnot have to be treated prior to be processed through the extrusion die.

Also the lack of humidity in the PET melt increases the PET resinoptical properties and performance at the rigid film manufacturingstage. Both end use properties achieved through this manufacturingprocess result in sheet quality, which are greatly important tothermoformers and end users. Also the trim and other waste generated aspart of the process is of high quality in terms of I.V. readings and canbe blended with virgin PET resins in the preparation process.

PET sheets produced by the above methods are manufactured at a lowercost, have a high structural homogeneity, enhanced optical propertiesand excellent mechanical strength. In the case of the manufacture ofitems directly from the reactor onto a rotary die, the results are thesame, except the products manufactured are not previously converted intosheets, but formed into their final configuration.

SUMMARY

Preferably, the sytem for making PET objects includes means for reactinga first PET precursor and a second PET precursor to produce a PET melt;means for flowing the PET melt to a valve having at least two outlets;means for flowing the PET melt from at least one of the at least twooutlets to at least one distribution manifold, each of the at least onedistribution manifold having at least two distribution lines; means forcontrolling individually the mass flow of the PET melt in each of the atleast two distribution lines independently of the other of said at leasttwo distribution lines; and means for forming the PET. objects from thePET melt. Preferably, the system further includes means for flowing thePET from one of the at least two outlets to a side chip stream forforming pellets. Preferably, the means for reacting takes place within atemperature range of from about 200° C. to about 330° C.

Preferably, first PET precursor is selected from the group consisting ofPure Terephthalate Acid (PTA) or Dimethyl Terephthalate (DMT) and thesecond PET precursor is Mono Ethylene Glycol (MEG) or Diethylene Glycol(DEG). In another aspect of the present invention, secondary precursors,such as Cyclohexanedimethanol (CHDM) may be used in combination with theprimary precursors, such as MEG. In this aspect, the final product is aglycolized polyester (PETG). Preferably, the system further includesmeans for reducing the acetaldehyde content of the PET melt. Preferably,the means for controlling individually the mass flow of the PET meltincludes means for controlling the pressure of the PET melt withpressure control loops prior to the forming the PET objects. Preferably,the PET objects are selected from the group consisting of PET articles,PET sheets, strapping, and architectural items. Preferably, means forforming PET objects further includes means for adding at least one sideextruder to produce a multi-layered PET sheet or object. Preferably, thesystem further includes means for producing a laminated structureselected from the group consisting of foil and EVOh structure.Preferably, the system further includes means for filtering said PETmelt prior to the forming the PET objects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of the system for making PET sheetsaccording to an embodiment of the present invention;

FIG. 2 illustrates block diagram of a die and co-extruder of the systemfor making PET sheets according to an embodiment of the presentinvention;

FIG. 3 illustrates a block diagram of a die and laminated sheetsubsystem of the system for making PET sheets according to an embodimentof the present invention; and

FIG. 4 illustrates a flow diagram of a process for making PET sheetsaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The term PET films generally means a rigid film of PET or APET of atleast 5 mils. This sheet can be converted into rolls of differentdiameters or directly slit into sheets. PET and APET resin are usedinterchangeably as the resin used to manufacture the APET rigid film.Like reference numerals are used to indicate like parts throughout thedrawings. FIG. 1 illustrates an embodiment 100 of a system for makingPET sheets. Precursors or raw materials are fed into the reactor 106 ofthe system for making PET sheets 100. In one embodiment, the precursorsinclude a feedstock of Pure Terephthalate Acid (“PTA”) or DimethylTerephthalate (“DMT”) 102 and a feedstock of Mono Ethylene Glycol(“MEG”) 104. In another embodiment, another glycol, such as DEG may beused. In another aspect of the present invention, secondary precursors,such as Cyclohexanedimethanol (CHDM) may be used in combination with theprimary precursors, such as MEG. In this aspect, the final product is aglycolized polyester (PETG).

In one embodiment, the two feedstocks 102 and 104 produce anintermediate bis-(2-hydroxyethyl) terephthalate, which may be convertedto polyethylene terephthalate by heating at a temperature above theboiling point of the ethylene glycol or the reaction mixture underconditions effecting the removal of the glycol or water. The feedstocks102 and 104 are reacted in the reactor 106 by esterification andpolymerization to produce the PET melt. The heating in the reactor 106may occur at a temperature as high as 325° C., if desired. Duringheating, pressure is reduced so as to provide rapid distillation of theexcess glycol or water. The final polyethylene terephthalate polymer mayhave an I.V., as measured in orthochlorophenol at 25° C., in excess of0.3 dl/gm. More preferably, the I.V. of the polymer ranges from about0.4 to about 1.0 dl/gm, measured in orthochlorophenol at 25° C. Stillmore preferably, the polyethylene terephthalate employed in the presentsystem for making PET sheets 100 has an I.V. of about 0.5 to about 0.7dl/gm as measured in orthochlorophenol at 25° C. The thermoplasticpolyester containing polymers of this present system for making PETsheets 100 have a preferred melting point in the range of from about200° C. to about 330° C. or more preferably from about 220° C. to about290° C. and most preferably from about 250° C. to about 275° C.

In one aspect, the present system for making PET sheets 100 produces PETsheets. In another aspect, the present system for making PET sheets 100is used to produce all types of products, including sheets, with allother types of molten polymers. Another exemplary molten polymer is alinear low density polyethylene (LLDPE) polymer. In addition tohomopolymers, the present system for making PET sheets 100 may be usedwith copolymers of PET, such as adding cyclohexane dimethanol (CHDM) inplace of the ethylene glycol or isophthalic acid in place of some of theterphthlate units. These are examples of slurry copolymers off the basereaction that can be utilized in this manufacturing process.

Many different kinds of additives can also be added into the PET melt,depending on the nature of the desired properties in the finishedarticle. Such additives may include, but are not limited to, colorants,anti-oxidants, acetaldehyde reducing agents, stabilizers, e.g. U.V. andheat stabilizers, impact modifiers, polymerization catalystdeactivators, melt-strength enhancers, chain extenders, antistaticagents, lubricants, nucleating agents, solvents, fillers, plasticizersand the like. Preferably, these additives are added into the reactor106, but may be added at other locations of the present system formaking PET sheets 100.

The PET melt is then fed via pipe 108 to a master pump 110 where it ispumped to a filter 114 via pipe 112. In this embodiment, the master pump110 feeds the PET melt throughout the distribution subsystem. The PETmelt is based through the filter 114 to clear the PET melt of anyforeign particles either introduced through the feed stream or producedby the reaction. Preferably, the filter 114 is used to screen out anylarge gels, degraded particles or extraneous material deleterious to thedownstream melt pumps or to the final product. Various grades of filtermedium or mediums (mechanical screens, sand, sintered metal, etc.) canbe used. The proper design (volume, pressure drop and residence time) ofthe filter 114 is important to maintain the proper pressure throughoutthe present system for making PET sheets 100.

The PET melt is then fed to a valve 118 via pipe 116. In this particularembodiment, the valve 118 is a four way valve including one inlet andthree outlets. Preferably, valve 118 may have any number of outlets tofit a desired application. The valve 118 feeds PET melt into a bypasschip stream 124. This stream produces PET pellets that are conditionedto produce low acetaldehyde PET. This material can be sold directly forbottles or utilized in a coextrusion process (FIG. 2) to produce amulti-layered film. Additionally, the valve 118 also feeds PET melt intotwo distribution manifolds 126 and 128 feeding a multitude of formingstreams. Although two distribution manifolds 126 and 128 are shown, oneor more than distribution manifolds can be used. Preferably, manifolds126 and 128 are designed to provide minimum residence time and flow ofthe PET melt through each down stream units such that the residence timeand pressure drop are optimized. Preferably, the lay-out, design, andsizing of the downstream equipment is considered in determining theresidence time and flow of the PET melt through the manifolds 126 and128.

Distribution manifold 126 feeds the PET melt to one or more acetaldehydereduction units 132 via pipes 130. Similarly, distribution manifold 128feed PET melt to one or more acetaldehyde reduction units 144 via pipes142. The acetaldehyde content of the PET is directly related to the timein each channel. Acetaldehyde reduction units 132 and 144 reduce theacetaldehyde content in the forming channels, pipes, or system topreferably less than 10 parts per million (“PPM”). If the pipes 108,112, 116, 120, 122, 130, and 142 has a sufficiently low residence timeto produce less than 10 PPM, then no acetaldehyde reduction units 132and 144 may be required.

The acetaldehyde reduction units 132 and 144 may include thin filmevaporators, vacuum degassing, acetaldehyde scavenger additions, or anyother process to reduce acetaldehyde in a continuous melt stream. Theacetaldehyde reduction units 132 and 144 can be, but not limited to, athin film device, a vacuum screw section, or an acetaldehyde additivefeeder with static mixer. In one aspect, the acetaldehyde reductionunits 132 and 144 may be any apparatus known in the art for generating alarge amount of surface area per unit volume and/or for rapidlyregenerating the exposed melt surface. The acetaldehyde reduction units132 and 144 should subject the liquid surface to a low partial pressureof acetaldehyde either by inert gas purging as described in U.S. Pat.No. 5,597,891, applied vacuum or both. The acetaldehyde reduction units132 and 144 may be a vented single-screw extruder (U.S. Pat. No.4,107,787), a vented twin-screw extruder (U.S. Pat. No. 3,619,145), arotating disk processor (U.S. Pat. No. 4,362,852), or device whichgenerates thin strands of polymer (U.S. Pat. No. 3,044,993), all ofwhich are incorporated herein by reference.

The acetaldehyde reduction units 132 and 144 may also include suitablemixers, such as static mixers, gear pumps, and/or single or multi-screwextruders, all of which are well known in the art. In one aspect, anacetaldehyde stripping agent is injected into the acetaldehyde reductionunits 132 and 144 by an injection nozzle (not shown) at a rate of about1.0 SCF/lb of the polymer or less. The activity of the mixer forms amultitude of small gas bubbles in the PET melt. The acetaldehyde andother by-products present in the PET melt diffuse into the gas. Suitablestripping agents that are inert to the PET melt include nitrogen, carbondioxide, C₁ to C₄ hydrocarbons, dehumidified air, and the noble gases.The more preferred stripping agents are carbon dioxide and nitrogen.Throughout the process, the PET melt is maintained at a temperaturegreater than the melting point of the PET melt, but preferably nogreater than from about 10° C. to about 15° C. higher than its meltingpoint.

In one embodiment, the acetaldehyde reduction units 132 and 144 includea vacuum section with a screw element in the line through the vacuumsection. The vacuum will reduce the acetaldehyde content and the screwelement will internally increase the melt pressure after the vacuumsection is passed. Preferably, the pressure is reduced during vacuumingto prevent the PET melt from going through the the vacuum port, then thepressure may be increased with the screw element.

The PET melt is then fed from the acetaldehyde reduction units 132 and144 to a plurality pumps 136 and 144 via pipes 134 and 142,respectively. The pumps 136 and 144 are used to produce a constantpressure into the die forming units 140 and 152 via pipes 138 and 150,respectively. The plurality of pumps 136 and 144 are required tomaintain a fixed pressure with minimial variation by balancing thepressure disturbances in the entire system. In one embodiment, the pumps136 and 144 are gear pumps which pass a known volume through with eachrevolution. The speed of the pumps 136 and 144 may be controlled by apressure sensor on the outlet side. As the pressure is reduced the pumps136 and 144 speed up and visa versa on high pressure.

In one embodiment, the present system for making PET sheets system formaking PET sheets 100 is a continuous process which is not shut downonce it is started. One way to control the mass flow of the PET meltthrough the present system for making PET sheets 100 is by adjusting themass flow of the feedstocks 102 and 104 into the reactor 106. A pressurefeed back loop can be used to control the valve 118. The valve 118 tothe bypass chip stream 124 can be opened more or less to modulate thePET melt going into each distribution manifold 126 and 128. The pumps136 and 148 are used to control the final pressure into the die formingunits 140 and 152. Nevertheless, due to the critical nature of thepressure entering the die forming units 140 and 152, it may be necessaryor preferably to add more than one pump at this point. The additionalpumps (not shown) may be used in tandem and are controlled by a pressurefeed back loop to change the mass flow of PET melt into the die formingunits 140 and 152 as the forming line changes speed or are shut down.Although a single pump can be used, the variation in pressure do to theinfluence of pressure changes from any other section in the entiredistribution system may not sufficient to maintain part dimensionaluniformity. As an example, it is preferable to maintain +/− 1 bar inpressure into a flat die to maintain proper control of the finishedsheet.

In one embodiment, the present system for making PET sheets 100 producesPET sheets in a continuous mode from PTA and MEG directly from the meltphase of the reactor 106 to an extruder die without passing through anitrogen treatment, an extruder and other steps and rolled or not in thelongitudinal direction. In another embodiment, the present system formaking PET sheets 100 flows the PET melt directly from the reactor 106and an extruder die onto rotary dies for the manufacturing of packagingmaterial and other items.

In one embodiment, the die forming units 140 and 152 are a three rollstacks or sir (air?) knife system. More preferably, the die formingunits 14 and 152 are a horizontal three roll stack system. Typically,down stream of the roll stack are auxiliary systems such as coaters,treators, slitting devices, etc. that feed into a winder. These unitsare properly specified to the individual leg of the manifold and to theoverall capacity of the reactor 106.

In another embodiment, another type of unit would be a low draw rotarydie that forms parts such as bottle caps or lids directly on the rotarydie from the formed sheet.

In one embodiment, there is one pump 110 feeding the manifold systems126 and 128. Preferably, at the end of each manifold leg, prior to thedie and sheet or rotary die, there are one or two individual pumps 136and 148, respectively. Preferably, pump 110 maintains the pressure intothe manifolds 126 and 128. This pump 110 is controlled by the pumps 136and 148. If the pressure drops the pump 110 will increase pressure. Ifthe pressure rises then either the pump 110 slows down or the PET meltmaterial is switched into the bypass chip stream 124 bypassing themanifolds 126 and 128. Preferably, if the manifolds 126 and 128 aregoing to be have a lower throughput for an extended period of time, suchas for several hours, then a signal will be given to the reactor 106 toslow the feed to compensate for the lower throughput. Where pumps 136and 148 include two pumps in series, the first pump of the multiple pumparrays is used to modulate the pressure in the manifolds 126 and 128,respectively. In this arrangement, the first pump in the series of pumpscomprising pumps 136 and 148 maintains a constant pressure head into thesecond pump in the series of pumps. Preferably, the multiple pumpsprovides highly dependent thickness control with a constant pressureinto the die forming units 140 and 152. The first pump will modulate anylarge swings in pressure. The second pump and each proceeding pump willfurther reduce any modulation down to less then +/− 1 bar after thefinal pump. This provides for the forming lines (outputs) to remainindependent so they can slow down, start stop or increase speedindependently of the other die forming units 140 and 152. The pressurecontrol loops with the bypass chip stream 124 will provide thisfunction. In one embodiment, the pumps are volumetric pumps as describedherein.

In one aspect, APET melt, which may be used to prepare the PET sheet, isproduced by melting PET pellets into an extruder and then dropping itonto a surface where the melt is formed into a sheet. In the case of thepreparation of items using a rotary die, the melt is passed through aextruder die and deposited directly onto a rotary die, where the itemsare manufactured.

In another embodiment, the mass flow of PET melt may be controlled bycontrolling the pressure of said PET melt with pressure control loops incommunication with the pumps 136 and 148 prior to the die forming units140 and 152 to control pressure and maintain pressure independently ofthe individual pipes 138 and 150 throughput requirements or what theother individual pipes 138 and 150 or flow channels are producing.

The pressure control logic controls the continuous slurry reactor 106whose response time is typically greater in magnitude than that at theoutput ends at the die forming units 140 and 152 to control thethickness of the final product or sheet. In one embodiment, this isaccomplished while having each output leg remain independent of theother output legs. In one embodiment, the control loop provides forsudden process upsets, such as starting or stopping of one of the outputlegs. In this embodiment, a bypass chip stream 124 allows for the chipproduction to increase or decrease based on any process upset. The upsetcan be a planned upset, such as stopping a line for maintenance, etc.,or unplanned upset, such as an equipment malfunction.

In addition to the above, the control loop preferably compensates forone leg increasing or decreasing speed while continuing the overallsystem for making PET sheets 100 in a steady state. The pump 100 andassociated valves (not shown) will react by diverting to or from thebypass chip stream 124. This may cause a brief spike or change inpressure that will be reacted to by the pumps 136 and 144 at the end ofeach manifold 126 and 128 that will then react to the pressure spike andmodulate it in a controllable and desirable fashion. In this embodiment,the individual pumps that comprise the pumps 136 and 144 will experiencethe pressure spike and react to it while the second pump in the serieswill experience the modulation of the upset magnitude that will besufficiently low as to be modulated out in the order of magnitude ofless than a second. In another embodiment, each line configuration isgoing to be different so individual schemes will apply to that system.Preferably, a combination of the manifolds 126 and 128, pumps 136 and144, and control loop provide an optimized PET melt pressure and flowthrough the pipes to the forming portions or die forming units 140 and152.

FIG. 2 shows an embodiment 200 of a co-extrusion subsystem to producemulti-layered sheet by adding a co-extruder 204 to the PET melt containtin pipe 138 or 150. The co-extruded material is fed from the co-extruder204 to a feed block 212 via pipe 202 along with the PET melt from theflow channels as described above. The feed block 212 then layers thematerials properly into the flat die 208. This feed block 212 orientatesthe streams producing a multi-layer stream, which is fed to a flat die208 via pipe 206 where it is extruded into the sheet forming section orPET sheet 210. The co-extruder 204 can use resin pellets from the bypasschip stream 124 or be a different material such as an adhessive tielayer or barrier resin, but not limited to these examples. Thisco-extrusion process may be added to any or all the die forming units140 and 150. In one embodiment, the size of the co-extruder 204 isdesigned relative to the pounds throughput required. In using aco-extruder 204 in the present system for making PET sheets 100,preferably, the added pounds of material added into the system must betaken into account to provide the required cooling capacity of the legof the present system for making PET sheets 100.

FIG. 3 shows an embodiment 300 of a subsystem to create a laminatedmulti-layered structure or PET sheet. The PET melt (either singlelayered or multi-layered coextruded) is fed through the flat die 208 viapipe 206 into the forming rolls 310 and 312. In one embodiment, anadditional film 304 is fed into the forming rolls 308 and 310. The heatfrom the PET melt stream bonds the additional film 304 into a coherentlaminated stucture 316. Additional rollers 306 and 308 may be employedfor guiding the additional film from the feed spool 302 to the formingrolls 312. In another embodiment, other materials such as metal foils,or EVOH film can be added to the laminating process. In yet anotherembodiment, other types of materials may be added to the laminatingprocess. Each of these unique structures then can be used for specificend applications.

Preferably, the design criteria for the subsystem to create a laminatedmulti-layered structure or PET sheet 300 is to provide the highestquality sheet from the lowest capital investment. The high throughput ofPET melt through the system for making PET sheets 100 requires gooddesign of cooling rolls so deflections do not occur. The ability tomonitor and control thickness of the PET sheets during cooling isimportant. In addition, the ability to change sizes and thicknesses ofPET sheets is important as well. Further downstream operations, such aswinding and slitting are also considered when using the laminatedmulti-layered structure or PET sheet 300.

As has been shown, the resulting product or PET sheet is determined bythe die forming units 140 and 152. This present system for making PETsheets 100 controls the die forming units 140 and 152 with suchprecision (as well as an extrusion system) that the objects produced bythis system are limited only by the creativity of the manufacturer.

In one embodiment, the present system for making PET sheets 100 controlsthe pressure from a continuous reactor 106 to multiple flow channels.Each channel is tied to a forming section producing different objects.Each flow channel acts as an individual extruder without an extruder. Inanother embodiment, a single pump 136 may be used if the pump dynamicsare accounted for in the process control algorithm.

In one embodiment, the present system for making PET sheets 100 impactsfavorably the mechanical and optical properties of the PET sheet beingmanufactured that will enable the PET sheet to be manufactured at alower caliper when being manufactured for packaging or other applicationsuch a sheets, strapping, architectural items.

The present system for making PET sheets 100 produces PET objects andarticles that have quality of trim and other waste generated as part ofthe manufacturing process will be of high quality such that it can beblended in high percentages with virgin PET melt without negativelyimpacting the final sheet quality and the need to increase caliper.

In addition to the aforementioned aspects and embodiments of the presentsystem for making PET sheets system for making PET sheets 100, thepresent invention further includes methods for manufacturing these PETsheets. FIG. 4 illustrates a flow diagram of an embodiment 400 of onesuch process. In step 402, a first PET precursor and a second PETprecursor as described above are reacted in a reactor to produce a PETmelt. Preferably, in this step, the known reactor capacity and a givenproduct mix of sheet thicknesses and widths are determined. From thisinformation the number of manifold legs is determined by considering thecooling capacity of each of the die forming units. The cooling capacitypreferably determines the maximum throughput of each downstream leg. Inone aspect, a bypass chip stream 124 can be introduced into the reactor106 at this step. In another aspect, a side stream of scraps from theprevious operation may be introduced into the reactor 106 at this step.

In step 404, the PET melt is filtered to remove impurities from the PETmelt. In step 406, the PET melt is flowed via a positive or negativedisplacement apparatus, such as a pump, to a valve having preferablymultiple outlets. In step 408, the PET melt is flowed from the valveoutlets to individual distribution manifolds connected to eachindividual valve outlet. In one embodiment, each of two outlets isconnected to a separate distribution manifold. Connected to eachdistribution manifold are at least one distribution lines thatpreferably terminate at a PET object die forming apparatus. In addition,one of the outlets of the valve feeds a side chip stream for forming PETpellets.

In step 410, the acetaldehyde content of the PET melt is reduced ifnecessary as described above. This may include using a vacuum sectionwith a driven screw section in the line to reduce the acetaldehydecontent in the PET melt. In another embodiment, a thin film degassingtechnique may be used to reduce the acetaldehyde content in the PETmelt.

In step 412, the pressure or mass flow of the PET melt is individuallycontrolled in each of the distribution lines by a pump or otherapparatus that controls the mass flow or pressure of the PET melt withineach distribution line separate from the other distribution lines. Instep 414, the PET melt in each distribution line is fed to a PET objectforming die or sheet forming subsystem.

Although there has been described what is at present considered to bethe preferred embodiments of the system for making PET sheets, it willbe understood that the present system for making PET sheets can beembodied in other specific forms without departing from the spirit oressential characteristics thereof. For example, additional pumps ordifferent combinations of pumps, other than those described herein couldbe used without departing from the spirit or essential characteristicsof the present system for making PET sheets. The present embodimentsare, therefore, to be considered in all aspects as illustrative and notrestrictive. The scope of the present system for making PET sheets isindicated by the appended claims rather than the foregoing description.

1. A method for making PET objects comprising: reacting a first PETprecursor and a second PET precursor to produce a PET melt; flowing saidPET melt to a valve having at least two outlets; flowing said PET meltfrom at least one of said at least two outlets to at least onedistribution manifold, each of said at least one distribution manifoldhaving at least two distribution lines; controlling individually themass flow of the PET melt in each of said at least two distributionlines independently of the other of said at least two distributionlines; forming said PET objects from said PET melt.
 2. The method ofclaim 1 further comprising: flowing said PET from one of said at leasttwo outlets to a side chip stream for forming pellets.
 3. The method ofclaim 1 wherein said reacting takes place within a temperature range offrom about 200° C. to about 330° C.
 4. The method of claim 1 whereinsaid first PET precursor is selected from the group consisting of PureTerephthalate Acid (PTA) and Dimethyl Terephthalate (DMT).
 5. The methodof claim 1 wherein said second PET precursor is selected from the groupconsisting of Mono Ethylene Glycol (MEG), Diethylene Glycol (DEG), andglycolized polyester (PETG).
 6. The method of claim 1 furthercomprising: reducing the acetaldehyde content of said PET melt.
 7. Themethod of claim 1 wherein said controlling individually the mass flow ofthe PET melt comprises: controlling the pressure of said PET melt withpressure control loops prior to said forming said PET objects.
 8. Themethod of claim 1 wherein said PET objects are selected from the groupconsisting of PET articles, PET sheets, strapping, and architecturalitems.
 9. The method of claim 1 wherein said forming PET objects furthercomprises: adding at least one side extruder to produce a multi-layeredPET sheet or object.
 10. The method of claim 9 further comprises:producing a laminated structure selected from the group consisting offoil and EVOh structure.
 11. The method of claim 1 further comprising:filtering said PET melt prior to said forming said PET objects.
 12. Asytem for making PET objects comprising: means for reacting a first PETprecursor and a second PET precursor to produce a PET melt; means forflowing said PET melt to a valve having at least two outlets; means forflowing said PET melt from at least one of said at least two outlets toat least one distribution manifold, each of said at least onedistribution manifold having at least two distribution lines; means forcontrolling individually the mass flow of the PET melt in each of saidat least two distribution lines independently of the other of said atleast two distribution lines; means for forming said PET objects fromsaid PET melt.
 13. The system of claim 12 further comprising: means forflowing said PET from one of said at least two outlets to a side chipstream for forming pellets.
 14. The system of claim 12 wherein saidmeans for reacting takes place within a temperature range of from about200° C. to about 330° C.
 15. The system of claim 12 wherein said firstPET precursor is selected from the group consisting of PureTerephthalate Acid (PTA) and Dimethyl Terephthalate (DMT).
 16. Thesystem of claim 12 wherein said second PET precursor is selected fromthe group consisting of Mono Ethylene Glycol (MEG), Diethylene Glycol(DEG), and glycolized polyester (PETG).
 17. The system of claim 12further comprising: means for reducing the acetaldehyde content of saidPET melt.
 18. The system of claim 12 wherein said means for controllingindividually the mass flow of the PET melt comprises: means forcontrolling the pressure of said PET melt with pressure control loopsprior to said forming said PET objects.
 19. The system of claim 12wherein said PET objects are selected from the group consisting of PETarticles, PET sheets, strapping, and architectural items.
 20. The systemof claim 12 wherein said means for forming PET objects furthercomprises: means for adding at least one side extruder to produce amulti-layered PET sheet or object.
 21. The system of claim 20 furthercomprises: means for producing a laminated structure selected from thegroup consisting of foil and EVOh structure.
 22. The system of claim 12further comprising: means for filtering said PET melt prior to saidforming said PET objects.
 23. A system for making PET objectscomprising: a reactor for reacting a first PET precursor and a secondPET precursor to produce a PET melt; a first pump to pump said PET meltto a four-way valve; at least one distribution manifold in communicationwith two of said outlets of said four-way valve; at least twodistribution lines in communication with each of said at least onedistribution manifold; an individual PET object forming die incommunication with each of said at least two distribution lines; and anindividual second pump in communication with each of said at least twodistribution lines and said PET object forming die for controllingindividually the mass flow of the PET melt in each of said at least twodistribution lines independently of the other of said at least twodistribution lines.
 24. The system of claim 23 further comprising: aside chip stream in communication with said other of said outlets forforming pellets.
 25. The system of claim 23 wherein the temperaturewithin said reactor is in the range of from about 200° C. to about 330°C.
 26. The system of claim 23 wherein said first PET precursor isselected from the group consisting of Pure Terephthalate Acid (PTA) andDimethyl Terephthalate (DMT).
 27. The system of claim 23 wherein saidsecond PET precursor is selected from the group consisting of MonoEthylene Glycol (MEG), Diethylene Glycol (DEG), and glycolized polyester(PETG).
 28. The system of claim 23 further comprising: an acetaldehydeunit for reducing the acetaldehyde content of said PET melt.
 29. Thesystem of claim 23 wherein said at least two distribution lines furthercomprises: means for controlling the pressure of said PET melt withpressure control loops.
 30. The system of claim 23 wherein said PETobjects are selected from the group consisting of PET articles, PETsheets, strapping, and architectural items.
 31. The system of claim 23wherein said PET object forming die further comprises: at least one sideextruder to produce a multi-layered PET sheet or object.
 32. The systemof claim 23 further comprising: a filter for removing impurities fromsaid PET melt prior to said PET object forming die.